1. Field
This invention relates to exercise machines such as treadmills, and more particularly to means for adjusting the endless belt surface of the treadmill to operate at differing preset slopes.
2. State of the Art
Exercise machines commonly known as treadmills are widely used for walking, jogging and running exercises. An endless belt moves on a track between two pulleys at a variable controlled speed typically between 0.5 and 6 miles per hour. The exercising person walks, jogs or runs at a speed matching the belt speed, to maintain a stationary position relative to the machine.
Treadmills typically include means to adjust one or both of belt speed and angle of inclination or slope to select a wide range of exercise difficulty. The slope or inclination may typically be varied between horizontal and a grade of 5 to 10 percent.
Various means are currently used for raising one end of the treadmill to achieve the desired angle of inclination. U.S. Pat. No. 4,759,540 (Yu et al.) discloses several scissor-jack arrangements for elevating the front end of a treadmill. A screwed rod with two oppositely threaded portions is rotated within two nuts to change their horizontal distance and raise the treadmill.
U.S. Pat. No. 4,792,134 (Chen) discloses a slope adjustment means comprising a shaft rotated by an electric motor through a gear arrangement, to pivotably raise or lower a pair of legs.
U.S. Pat. No. 4,749,181 (Pittaway et al.) describes a treadmill with an electrically driven slope changing apparatus. Nuts are rotated on vertical non-rotating screws to change the elevation.
U.S. Pat. No. 4,776,582 (Ramhorst) shows an exercise treadmill which uses a swing frame with a vertically adjustable pivot axis. The swing frame is pivoted forward to a position where opposed trunnions may be inserted into spaced cutouts to vary the height. The apparatus is relatively complex to fabricate, and thus expensive.
The foregoing patents describe relatively complex devices for adjusting the slope of the treadmill. Two of the machines use an electrical motor and are thus relatively expensive. None of the prior art devices easily or simply achieve several accurately preset angles of inclination or slope.